1. Field of the Invention
This invention generally relates to the measurement of power consumption by non-intrusive and self-powered measurement of power, and more specifically to management of thermal effects on self-powered measurement devices.
2. Prior Art
In a typical electricity distribution system, power is provided through a main circuit breaker and a device for measurement of the power consumption of the entire electrical network connected thereto. However, typically, the main power line is then connected to a plurality of circuit breakers, each feeding a smaller section of the electrical network with its specific power requirements. The circuit breaker is adjusted to the amount of maximum current that may be used by this electrical sub-network. In industrial and commercial applications, hundreds of such circuit breakers may be installed, each controlling a section of the electrical network. Even in smaller locations, such as a house, it is not unusual to find tens of circuit breakers controlling various electrical sub-networks.
Non-intrusive measurement of current through a power line conductor has well known principles. A current transformer (CT) of sorts is created that comprises the primary winding as the power line conductor and the secondary providing an output current inversely proportionate to the number of windings. Typically such systems are used for measuring currents in very high voltage or current environments, for example, as shown in Gunn et al. in U.S. Pat. No. 7,557,563. These types of apertures are useful for main power supplies. Using such devices, or power meters for that matter, is deficient for the purposes of measuring relatively low currents in an environment of a plurality of circuit breakers. Providing wireless telemetry on a singular basis, such as suggested by Gunn et al., and other prior art solutions, suffers from deficiencies when operating in a noisy environment. In some cases such sensors are self-powered, i.e., draw their power for operation from a primary current flowing through the CT. The energy is harvested from the magnetic field and is used for the operation of the sensor. Such sensor may operate over relatively small range of currents, as an example 0.5 A to 25 A. However, in other cases a much large current range is required, for example 0.5 A to 250 A. The latter case brings forward particular challenges not addressed by the prior art.
Transformation of energy is never one hundred percent efficient and as a result heat is dissipated. This happens in both low and high primary currents over the entire primary current range (for example, and without limitation, the range of 0.5 A to 250 A). However, it would be appreciated that as currents are higher the heat dissipation of components of the device is higher. The higher the power dissipation of a device harvesting energy the more likely it is that overheating may occur. Such overheating, especially in the confined surroundings of a circuit breaker enclosure, may result in a safety hazard. For example, overheating of the electrical wires may lead the insulation layer to become brittle, leading to exposure of the conductive wires and then create hazardous shortcuts in the electrical system. Moreover, standards such as EN60010 limit any device temperature to 70° C. for that reason. It would be advantageous if a solution may be provided for avoiding such overheating situations of such measurement units.